Open source: add new projects and section on incubated projects

I've created an "Incubated" section to deal with projects like sass-mq that have moved beyond the organisation and added @rtyley 's GitHub robots which were an oversight from the original list.

In some ways it would also be good to list projects with contribute to as well as a kind of endorsement of projects we won't build ourselves.
@gidsg Thanks, fixed on master.